1. Field of the Invention
The present invention relates to a presser foot drive device in a sewing machine.
2. Description of the Prior Art
Conventionally, two types of presser foot drive devices have been proposed for vertically reciprocally moving a presser foot in a sewing machine. One type of the devices is constructed to move the presser foot in response to movement of a needle bar, and the other type is constructed to move the presser foot independently of the needle bar. In case of the latter type, the rotation of a main shaft for driving the needle bar and a shuttle is converted into the reciprocal movement of the presser foot by a cam mechanism or a link mechanism.
In the prior art presser foot drive devices, even if they are of the latter type for independently driving the presser foot, the stroke of vertical movement of the presser foot as well as the timing of its vertical movement relative to the movement of the needle bar is substantially fixedly determined by the design of the sewing machine. Thus, the presser foot is moved regardless of the sewing situation or the material of a work fabric. This may produce unpleasant vibrations or noises or may cause breakage of a sewing thread.